15 September  2016, 10:00

Effects of the nozzle exit boundary layer on hot-jet mixing

Abstract: The main motivation of the research effort reported here was passive protection of airplanes against an enemy’s heat seeking missiles. The stated goal was to reduce the temperature of a jet engine exit flow by means of the hot-jet rapid mixing with the ambient air, and no penalty of the jet engine thrust was allowed. The focus of the first phase of this project was to explore the properties of high-speed free jets and demonstrate that it is possible to enhance jet flow mixing by flow excitation. Inconsistencies in hot-jet responses to flow excitations were investigated in the second phase of this project. It was shown that the jet receptivity to flow excitation is strongly dependent on a character of the nozzle exit boundary layer. Finally, it was proven that the decisive factor controlling the jet receptivity is the velocity gradient across the exit boundary layer. There were also side byproducts of this research effort. First, it was an improvement in the high-frequency stroboscopic visualization of large-scale turbulent structures in free jet flows. The second innovation was the development of a new methodology for conditional sampling of random laser velocimeter data. 

17 August  2016, 10:00

Rotation-free parametrization and isogeometric analysis of shear deformable plates and shells

Abstract: Structural theories for static and dynamic analysis of shear deformable plates and shells (Reissner-Mindlin type) usually employ independent degrees of freedom for displacements and rotations. It is shown how equivalent models can be developed based on displacement degrees of freedom only. In the context of finite element formulations this has the advantage that transverse shear locking can be intrinsically avoided within a standard displacement-based concept, regardless of the underlying function spaces used for discretization.

As in this context higher continuity of the shape functions is required, a natural way is to incorporate such theories into the isogeometric concept, using NURBS (non-uniform rational B-splines) as shape functions. Corresponding shear-deformable shell finite element formulations for geometrically linear and non-linear applications are presented and their performance is demonstrated with the help of numerical examples. 

2 June 2016, 10:00

Mathematics of fluids in motion

Abstract: We discuss the recent development of the mathematical theory of fluid dynamics, classical and new open problems and possibilities of their solution. Special attention is paid to the recent results on well and/or ill-posedness of problems describing inviscid fluids. In particular, several modern concepts of solutions are examined: Weak, very weak, measure-valued etc.

4 May 2016, 10:00

Development of Human Artificial Vocal Folds

Abstract: Voice production is a complex physical process, which involves airflow coming from the lungs, selfoscillating vocal folds and acoustics of the resonance cavities of the human vocal tract. The vocal folds, excited by the airflow, generate a primary sound which propagates in the airways of the vocal tract modifying its spectrum and producing the final acoustic signal radiated from the mouth. Understanding basic principles of voice production is important for detection of laryngeal pathologies and treatment of laryngeal disorders. The physical models of voice production are important tools not only for experimental verification of computational 3D finite element models of phonation, but also for development of the vocal folds prosthesis. The study compares results of in vitro measurements of phonation characteristics performed on originally developed 1:1 scaled artificial models of human vocal folds. The measured aerodynamic, vibration and acoustic characteristics of the last models are comparable with the values found in humans..

6 April 2016, 10:00

Stochastic Self-Organization in Inner Structure of Vehicular Systems

Abstract: History of traffic science is relatively short. Generally, it is meant that the first scientific article is the essay of Professor Bruce Greenshields dated to 1934. The factual beginning of systematic scientific discipline (called Transportation Science) is the year 1992, when the field accelerated by many famous publications. Nowadays Transportation Science is very well anchored in the portfolio of scientific disciplines (associated MIF is 1.377). For the purposes of this seminar talk we choose a theme of predictions for statistical properties of traffic flows and detection of surprising relations in traffic microstructure.
In this talk we will show that macroscopic self-organization of traffic streams (e.g. spontaneous traffic congestions) is projected into evolution of stochastic properties detected for vehicular micro-quantities. Furthermore, we will demonstrate that there exists a smart and uncomplicated way how to predict such microscopic effects.

Animal Flight

Abstract: Unlike airplanes, animals must have either flapping wings (birds, bats) or oscillating wings (insects). Only such wings can produce both lift and thrust, provided the animal has sufficient muscle power.
To fly, wings impart downward momentum to the surrounding air and obtain lift by reaction. How this is achieved under various flight situations (cruise flight, hovering, landing, etc.), and what is the role of the wing-generated vortices in producing lift and thrust is discussed (both for birds and insects).
Bird wings have several possibilities how to obtain the same functions as airplane wings. Birds have the capabilities of adjusting the shape of the wing according to what the immediate flight situation demands, as well as of responding almost immediately to conditions the flow environment dictates.

FLUIDIC OSCILLATORS FOR ALGAE CULTIVATION and their role in geopolitic stability

Abstract:
Our civilisation is extremely dependent on cheap liquid fuel used for transportation. Until roughly the end of 19th century people used to work in their respective dwelling places. Now they commute in huge numbers every day. Food and other goods travels hundreds (if not thousands) of kilometres between production and use. This model is increasingly adopted by developing most populated countries (China, India). Fossil fuel sources, on which this all depends, is produced – at an increasingly high cost – in politically unstable regions. No wonder research grant providers are willing to support financially the research promising renewable petrol as its result. The starting point are algae – primitive, often unicellular plants capable to produce by photosynthesis - from H in water and CO2 taken from air - hydrocarbon compounds, processing of which into biofuels brings no difficulty in principle – after all, the fossil oil was produced the same way from algae millions of years ago. Additional benefit would be the whole process being carbon neutral so that removal of CO2 from the atmosphere would suppress the global warming. Algae may be also a starting point of a food chain, solving another global problem.
The difficulty is so far the price of the crude oil from algae being higher than the fossil one. The key factor for success is making more efficient every step in the process. One of perhaps small but nevertheless important contribution towards the goal is more efficient diffusion transport of CO2 into the algae in bioreactors. Suggested solution is generation of sub-millimetre sized microbubbles by placing a fluidic oscillator into the gas inlet. The research grant project investigated in the Institute of Thermomechnaics enabled recently testing a number of alternative oscillator designs.

Discontinuous Galerkin method for the solution of elasto-dynamic, compressible flow and fluid-structure interaction problems

Abstract:
This lecture will be concerned with the numerical solution of dynamic elasticity and compressible flow. We consider the linear case as well as the nonlinear St. Venant-Kirchhoff model. The space Discretizat on is carried out by the discontinuous Galerkin method (DGM). For the time discretization several techniques are proposed and tested. As the best method the DG discretization both in space and time appears. The discontinuous Galerkin method is also used for the numerical solution of compressible flow in time-dependent domains, formulated with the aid of the arbitrary Lagrangian-Eulerian (ALE) method. It will be shown that this method allows the solution of compressible flow with a large range of the Mach number. Then the developed methods are combined and used for the numerical simulation of vibrations of elastic bodies induced by compressible flow. The applicability of the developed techniques will be demonstrated by several numerical experiments.
The results were obtained in cooperation with M. Balázsová, J. Česenek, M. Hadrava, A. Kosík and J. Horáček.